The invention relates to an arrangement for damping oscillation of a loading member in a crane comprising a trolley, a hoisting mechanism located in the trolley, at least one hoisting rope suspended from the hoisting mechanism, a loading member fastened to the hoisting rope, the arrangement for damping oscillation of a loading member comprising a vertical guide projection arranged in an upper part of the loading member, a guide tube rigidly fastened to the trolley for receiving the guide projection, damping members arranged in the guide tube and comprising elastic guide roll structures arranged to engage around the guide projection, each guide roll structure comprising a roll frame and a guide roll installed therein.
Accelerations and decelerations of a crane are mainly responsible for oscillations of a loading member of the crane. This oscillation may be minimized by driving the crane at a constant speed or sufficiently slowly. Research abounds for damping or eliminating oscillations of a loading member of a crane and a load attached thereto by using various computer programs or speed control methods, e.g. in U.S. Pat. No. 5,219,420. In some cases, particularly in container cranes, oscillation has been suppressed by means of auxiliary ropes and auxiliary drums, cf. for instance U.S. Pat. Nos. 5,769,250 and 7,287,740 as well as DE Patent 1207578.
In many applications also pneumatic or hydraulic dampers are used, cf. for instance GB Patent 1542821. However, when using process cranes in connection with heavy loads, such as vacuum hoists including loading members suspended therefrom, the cranes have to be driven at high speeds required by the course of the process. When the commodity to be moved is then e.g. a paper roll or a corresponding product, it is at high risk of being damaged if the liquids used in the crane leak to the product being moved. Tilting due to the influence of lateral forces may be particularly dangerous when using the aforementioned vacuum hoist, i.e. an underpressure-operated loading member, in which case the load may at worst come off the loading member.
U.S. Pat. No. 5,165,556, in turn, describes a device for damping oscillation of a loading member, comprising downward-pointing brackets attached to the bottom of a trolley. A load is lifted in place between these brackets, and the load is retained rigidly in place while driving the crane, whereby oscillation of the loading member and the load attached thereto is prevented. Such damping systems are expensive, and they require a lot of material and space. The damping of this type has a further disadvantage in that when the loading member is lifted at a high speed between the brackets, a gap formed by the brackets for the loading member has to be wide, which may lead to post-oscillations between the brackets. When the loading member has then been supported rigidly between the brackets, accelerations of the trolley directly influence the load attached to the hoisting member. These lateral forces move the structure, and the forces become large abruptly. This may lead to malfunction or increased risk of collision, particularly when handling large paper rolls, for instance, when the rolls are kept in place by means of a vacuum hoist. The endurance of joints is also at risk, and service is expensive.
From documents JP 08268682 A and KR 20010057393 A, centering of a loading member to a trolley of a crane by means of conical surfaces is known. Therein, a conical loading member centering piece is mounted immovably in the trolley. In the first-mentioned document, the conical surface of the loading member simultaneously serves as a damper.
Document DE 10105261 A1 also discloses centering and interlocking means between a loading member and a trolley as well as vertical damping means provided in the trolley for damping a centering event.
From Finnish Patent Application No. 20115289 is known an arrangement wherein a guide part is arranged in the trolley for receiving a guide projection of the loading member, the damping members connected thereto being arranged in a separate support frame which, in a hoisting direction of the hoisting member, is guidable into its place in a dock arranged underneath the trolley and which is lowerable off the dock, onto the loading member. The guide part is formed as a floating guide tube structure, and the damping members comprise a plurality of side damping modules connected between a side wall of the guide tube structure and the support frame, around the guide tube structure for damping horizontal movement of the guide tube structure. Further, a support joint is arranged in an upper part of the support frame, from which the guide tube structure is suspended. This structure is complex and thus quite challenging to implement in its entirety.
In SU 502830 A1, a load is lifted into a tube downwardly extending from a trolley, wherein the load is supported laterally in the tube by means of suspended wheels provided at ends of lever arms.